Shipping price didn't posted in Facebook API

Question

I am trying to post my products of Laravel eCommerce websites to Facebook Marketplace using API. The product is listed on Facebook but all products posted with free shipping even though I sent shipping costs by API from Laravel to Fackebook.

This is the code base:

$XML .= '<item>
    <g:id>' . $GPP->id . '</g:id>
    <g:title>' .$cleanedTitle. '</g:title>
    <g:description>' . strip_tags($cleanedDescription) . '</g:description>
    <g:availability>in stock</g:availability>
    <g:condition>new</g:condition>
    <g:price>' . html_entity_decode($GPP->product_price) . ' USD</g:price>
    <g:link>' . html_entity_decode($GPP->ebay_product_url) . '</g:link>
    <g:image_link>' . html_entity_decode($GPP->image) . '</g:image_link>
    <g:brand>' . $this->removeSpecialCharcters($GPP->brand) . '</g:brand>
    <g:quantity_to_sell_on_facebook>' . html_entity_decode($GPP->stock) . '</g:quantity_to_sell_on_facebook>
    <g:shipping>
        <g:country>US</g:country>
        <g:service>Standard</g:service>
        <g:price>'.$GPP->shipping_charges.' USD</g:price>
    </g:shipping>
    <g:google_product_category>' . $this->removeSpecialCharcters($google_product_category) . '</g:google_product_category>
    </item>';

Could you help me?

I am trying to be clear Facebook listing API issue. I am expecting to get the exact code from experienced developers